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In a feat of synthetic inorganic chemistry, researchers have made the first methylenedistibiranes—three-membered rings that have two antimony atoms and a carbon atom. Researchers led by Alessandro Bismuto at the University of Bonn and Antonio Frontera at the University of the Balearic Islands were able to crystallize the methylenedistibiranes and characterize them using X-ray crystallography (J. Am. Chem. Soc. 2025, DOI: 10.1021/jacs.4c15626).
Examples abound of rings that feature multiple nitrogen atoms—the lightest of the pnictogen elements. There are triazoles, which snap together in the classic, copper-catalyzed click chemistry reaction, and tetrazoles, which are motifs that can be found in antifungal compounds. But making similar heterocycles from heavier pnictogen elements like antimony and bismuth is challenging because the orbital overlap trends and energies change dramatically as one moves down the pnictogen column in the periodic table.
Bismuto says he and his colleagues were interested in making inorganic rings with multiple antimony atoms since they reasoned that such heterocycles would be reactive compared with linear Sb=Sb, which is not particularly reactive.
First, the chemists used a [3 + 2] cycloaddition between distibene and diazoolefins to make diazadistiboylidenes—five-membered rings that contain two antimony atoms, two nitrogen atoms, and a carbon atom. Bismuto says he was surprised how well this reaction worked, as there are only a few examples of small rings with multiple antimony atoms.
Reacting one of the diazadistiboylidenes with methyllithium produces an Sb–Sb anion, which the chemists were able to crystallize and characterize with X-ray crystallography. Irradiating the diazadistiboylidenes with light produced the three-membered-ring methylenedistibiranes.
“It’s extraordinary that they’re stable,” Bismuto says of the methylenedistibiranes. A version of this three-membered ring with nitrogen atoms instead of antimony has never been characterized. What’s more, one of the methylenedistibiranes reacts with carbon dioxide to generate a five-membered ring with two antimony atoms, two carbon atoms, and an oxygen atom.
Robert J. Gilliard Jr., an inorganic chemist at the Massachusetts Institute of Technology who was not involved in the work, says it’s rare and synthetically challenging to make heterocycles containing two heavy pnictogens like antimony. He is particularly impressed with the synthesis of the three-membered rings. “I expect that the methylenedistibirane will continue serve as a key reagent in the design of unprecedented heavier main-group element-containing heterocycles where their properties remain largely unknown,” he says in an email.
Bismuto says his group plans to continue making rings with heavier pnictogens—inspired in part by his surname, which means “bismuth” in Italian.
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